After the terminal metal bond pads are defined and etched on a semiconductor wafer, a passivation layer, generally SiO2 and SiN, is deposited on the wafer to protect the bond pads from the subsequent manufacturing process steps. In some products, a cost-effective polyimide, one kind of photoresist coated on plasma enhanced SiN (also referred to as PESN, which is a SiN film deposited using plasma enhanced chemical vapor deposition (CVD) process), is used to define the pattern of passivation layer and remains as residue on the wafer surface after passivation removal etching step. The residue left behind by the cost-effective polyimide is fluorine rich and the fluorine reacts with aluminum of the bond pads, producing AlxFyOz. Fluorine acts as an oxidizing agent and produces undesirable oxide deposits, AlxFyOz, on the bond pads. The AlFO3 deposits on the bond pads are not desirable because they result in non-optimal wire bonds and cause the affected wafers to fail quality control wire-bondability testing. This type of defects are non-reworkable and the wafers are scrapped.
Another source of the troublesome AlFO3 oxide desposits are associated with the etching of the silicon nitride protective passivation layer from the wafer during a pad mask patterning step at the end of the wafer processing. The silicon nitride passivation layer is etched with a dry/plasma etch performed in fluorine containing gases, such as CHF3, CF4, C2F6, C2F2, C4F8, etc. After a wafer has undergone the pad mask patterning step, residual fluorine may remain on the bond pads from the fluorine containing etch chemicals used in the dry/plasma etch process. This fluorine residue on the aluminum-containing bond pads produces undesirable oxide deposits, AlxFyOz.
One known solution to this problem is removing the AlxFyOz oxide deposits by argon plasma etching in the presence of a plasma enhancing carrier gas, such as carbon dioxide, or an inert gas, such as, helium, xenon, neon, krypton, etc. However, this argon plasma etching is a physical etching method and does not always satisfactorily remove the AlxFyOz oxide deposits.